This study investigated the environmental effects of two common emerging contaminants, sulfamethazine (SMZ) and sulfamethoxazole (SMX), and their mixture using a green microalga, Scenedesmus obliquus. The calculated EC50 values of SMZ, SMX, and their mixture (11:1 wt/wt) after 96 h were 1.23, 0.12, and 0.89 mg L-1, respectively. The toxicity of the mixture could be better predicted using a concentration addition model than an independent action model. The risk quotients of SMZ, SMX, and their mixture were >1 during the experiment, indicating their high potential risks on aquatic microorganisms. Despite their toxicity, S. obliquus exhibited 17.3% and 29.3% removal of 0.1 mg L-1 and 0.2 mg L-1 after 11 days of cultivation. The changes of SMZ and SMX removal were observed when combined, which showed a significantly improved removal of SMZ (up to 3.4 folds) with addition of SMX (0.2 mg L-1). The metabolic pathways of SMZ and SMX were proposed according to mass spectroscopic analysis, which showed six metabolites of SMX and seven intermediates of SMZ, formed as a result of ring cleavage, hydroxylation, methylation, nitrosation, and deamination.
Bibliographical noteFunding Information:
This study was supported by National Research Foundation of Korea (NRF) grants funded by the Ministry of Education, Science, and Technology (MEST) of the South Korean government (No. 2017R1A2B2004143 ), and the Doosan Yonkang Foundation .
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Environmental Chemistry
- Waste Management and Disposal
- Health, Toxicology and Mutagenesis